When fatty acids cannot pack together tightly enough to make a solid fat, they have?

When fatty acids cannot pack together tightly enough to make a solid fat, they have fewer hydrogen atoms.
Hydrogen atoms are responsible for this - it is thanks to them that fatty acids merge in order to create a solid fat. If there are not enough hydrogen atoms in the body, this operation will not be possible, and thus these acids will remain acids.

A. mitochondrion b. nucleus